Various processes are already known for producing mechanical structures in semiconductor wafers. A differentiation between bulk processes and surface processes is made in this case. A bulk process is described in the German patent disclosure DE-OS 40 00 496, and corresponding WO 91/03074, published 7 Mar. 1991, for example, where recesses are etched into the surfaces of a semiconductor body with the aid of photographic masking technology, and paddles are exposed by undercutting ridges and etching the back. In the bulk process, the largest portion of a wafer is removed by an isotropic etching process in order to obtain the desired mechanical structure. This has the disadvantage that after etching the wafer has structures which are sensitive to breaking and must be treated accordingly. Furthermore, process-related inner stresses in the structures can lead to mechanical deformations which make further processing much more difficult.
A surface treatment process is described in "Surface Micromachining Process for Electrostatic Microactuator Fabrication" by Theresa A. Lober and Roger T. Howe, IEEE 1988, in which structured auxiliary layers are applied to the surface of a silicon wafer and form pedestal-like protrusions on the surface. Polysilicon is deposited on top of these pedestal-like protrusions, so that the polysilicon layer is partially in direct connection with the surface of the silicon wafer. By subsequent removal of the auxiliary layer, overhanging polysilicon cantilevers are created on the surface of the silicon wafer. With this process, the actually mechanically stressed structures cannot be made of mono-crystalline silicon, which has disadvantageous effects on the expected long-term stability.
A process is also known from the Journal of Electrochemical Society, Extended Abstracts, Vol. 86-1, Masaru Shimbo, Kazuyoshi Furukawa, Kyoshi Funkunda, "A Newly Developed Silicon to Silicon Direct Adhesion Method", by means of which silicon wafers can be bonded to each other without requiring an intermediate layer for this.